1. Field of the Invention
This invention relates to air displacement pipetters.
2. Description of the Related Art
Air-displacement array pipetters are used extensively in the life-science and biotechnology arenas. These are designed to pipette in the Microliter range into and out of 96, 384, and 1536 assay plates that conform to the SBS microplate standard.
As shown in FIG. 1, a typical array pipetter in the prior art consists of two parts. The first is a cylinder block 20 into which 96 or 384 pistons 22 are inserted into corresponding cylinders. The second is a tip array carrier 26 with pipetting tips 28 welded thereon. The tip array carrier 26 is mated to the cylinder block 20 with o-rings 30 to seal the tips 28 to their corresponding cylinders. This mating can be done statically by bolting the tip array carrier 26 to the cylinder block 20 or dynamically by using a robotic or other motorized mechanism to pick up the carrier 26 and fasten it to the cylinder block 20. In use, the pistons 22 are coupled at their top ends to a robotic mechanism (not shown) that raises and lowers the pistons (typically all at once) to perform pipette operations to and from wells of multi-well plates. Typically, a pipetter includes an array of 96 or 384
There are many disadvantages to this basic design. For example, a large number of o-rings 30 are needed to seal the tip array carrier 26 to the cylinder block 20. When the array carrier 26 is removed from the cylinder block 20, many of these o-rings 30 may stick to the mating surface on the cylinder block 20 and are thus removed from their seat grooves in the array carrier 26. If automated tip array changing is implemented, any such loss of o-rings is unacceptable, as it will cause at least a partial loss of sealing. Even in the case of static mating, the situation is far from ideal because installing 96 or especially 384 small o-rings 30 is a burdensome task for the user.
Furthermore, welding the tips 28 to an array carrier 26 results in a very rigid architecture. If one tip is damaged, the entire array carrier has to be replaced. Moreover, the array of 96 or 384 tips has to be used in its entirety. Selective pipetting to or from a subset of wells in a plate is not possible. For example, to perform serial dilution one may want to pipette from one row of wells to another row. This is impossible with a welded array carrier 26 that carries a complete rectangular array of tips 28.